In a context of economic constraints, reducing the herd replacement costs represents a way to improve the economic efficiency of the dairy sector. Studies reported that heifers calving between 23 and 24.5 ... [more ▼]

In a context of economic constraints, reducing the herd replacement costs represents a way to improve the economic efficiency of the dairy sector. Studies reported that heifers calving between 23 and 24.5 mo of age achieved the highest economic return. However, the heifer has to be well developed to guarantee milk performance, calving ease and low stillbirth rate. Monitoring growth, by Heart Girth (HG) measurements, constitute a convenient way to evaluate the feasibility to inseminate heifers early. The aim of this study was to analyse the relationship between HG, age at first calving and milk production at first lactation. HG measurements of 704 Walloon (Belgium) Prim Holstein heifers have been recorded, every 3 months, during 2 years (2006 – 2008). The impact of development, at key-ages (from 3 to 24 mo, every 3 mo), on age at first calving and first lactation yield, was determined using analysis of variance. Mean total milk production in February 2010 (n = 319) rose to 7686 ± 1388 l/365 days of lactation, for a mean age at first calving (n = 421) of 27.4 ± 3.5 mo. These preliminary results suggest a positive correlation between growth performances and first calving age. Heifers with a better conformation (HG > 2.5 % of the French reference) calved significantly earlier than smaller animals. For instance, a lack of conformation at 15 mo implied a delay at first calving of 4.1 mo of age. HG measurement should therefore constitute a preferential tool of management of heifers herd. First lactation yield was significantly higher (950 l/365 d) for heifers calving older (> 30 mo) comparatively to early calving animals (24 mo). These results do not correspond to those related to larger samples in Wallonia. No significant relation could state, at this time, a direct relation between growth development and first lactation yield. Lactation data are still collected to complete this study. [less ▲]